A nanometer-scale pore can be used to determine a single molecule as it passes through the pore. Nanopore sensors have, for instance, have allowed fundamental studies on single biopolymers and have shown promise in a variety of biosensing applications. Nanopores can probe chemical interactions between DNA and other molecules because these interactions often substantially modify the structure of a DNA molecule. For example, oligonucleotide hybridization probes bind to specific DNA target sequences and create bulges that are easy to detect when they pass through a nanopore. However, additional devices and methods are still needed.